php - how to sum a value from 3 dimensional array

问题

I have data as below :

Array
(
    [1] => Array
        (
            [A] => Array
                (
                    [AA] => 3
                    [AB] => 5
                )

            [B] => Array
                (
                    [BA] => 2
                )

    [2] => Array
        (
            [C] => Array
                (
                    [CA] => 4
                )

            [D] => Array
                (
                    [DA] => 1
                    [DB] => 2
                )
        )

    [3] => Array
        (
            [E] => Array
                (
                    [EA] => 1
                    [EB] => 2
                    [EC] => 3
                )

            [F] => Array
                (
                    [FA] => 0
                    [FB] => 7
                    [FC] => 7
                )
)

I want to sum the value and this is my expectation :

Array(
    [1] => 10        
    [2] => 7
    [3] => 20
)

Here is my code that I used for summing the value :

$total[$country_id][$province_id][$city_id] = $amount;

$result = array();
foreach( $total as $key => $val ){
         $total[$key] = array_sum ( $val );
}

can someone explain what is wrong with my code or explain how foreach work? because the result of my code is 0 and actually I just studied around 1 week about foreach. Thanks

回答1:

As you want to know more about foreach, here is a more verbose solution using it :

$total = 0;
$totalByCountry = [];

// iterate over each country
foreach ($arr as $countryId => $provinces) {

    $totalByCountry[$countryId] = 0;

    // iterate over each province
    foreach ($provinces as $provinceId => $cities) {

        // iterate over each city
        foreach ($cities as $cityId => $value) {
            $totalByCountry[$countryId] += $value;
            $total += $value;
        }
    }
}

Result of var_dump(totalByCountry) :

array (size=3)
    1 => int 10
    2 => int 7
    3 => int 20

Result of var_dump($total) :

int 37

-- edit --

In real world project, you better be less verbose and use php functions made for this kind of situation like array_walk_recursive(), as in Philipp Maurer and Firoz Ahmad answers.

回答2:

The problem with your foreach is, that your array is three layers deep, while your foreach only traverses the first and array_sum() only calculates the second layer.

An example of your foreach:

$total = [
    0 => [
        'A' => [
            'AA' => 1,
            'AB' => 2
        ],
        'B' => [
            'BA' => 3,
            'BB' => 4
        ]
    ]
];

foreach( $total as $key => $val ){
    $total[$key] = array_sum ( $val );
}

The foreach will iterate over the $total array. This is the iteraton for the example:

1. $key = 0; $value = ['A'=>['AA'=>1,'AB'=>2], 'B'=>['BA'=>3,'BB'=>4]]
   In your loop, you then call array_sum() on $value. array_sum() adds the children of the provided array together, if they are numeric. Sadly $value is a two dimensional array and its children are arrays, so they are not numeric. That is why 0 is returned for it.

---

A solution to your problem would be to use the array_walk_recursive() function, that traverses inner arrays and calls a function upon them, that you can specify:

$sum = 0;
array_walk_recursive($total, function($value) use (&$sum) {
    $sum += $value;
});

The specified function adds the value of each leaf in your array to the specified variable $sum, that is given by reference to the function.

回答3:

print the $total,When coming to the foreach, $val is an array. so when calling array_sum function, it sums the first array and assign the total to a new array's first element. That is how this is working. The reason why you code is not working, there should be a foreach outside the foreach that you have been provided. Remove this foreach from above foreach's scope.

<?php

$x=[0=>[1,2,3],1=>[2,3,4]];

$result = array();
foreach( $x as $key => $val ){
       $total[$key] = array_sum ( $val );
}
var_dump($total);
?>

If your array is 3 dimentional Code is like this,

$y=[0=>[0=>[1,2,3],1=>[3,4,5]],1=>[0=>[5,6,7],1=>[8,9,10]]];

$result = array();
foreach( $y as $vals ){
   foreach( $vals as $key => $val ){
        $total[$key] = array_sum ( $val );
   }
}
var_dump($total);

回答4:

To achieve your desired output, you at first should iterate over your array and check if there exists any sub array then, again traverse all array members by using array_walk_recursive() function

<?php

    $arr = [
        [
            'A' => [
                'AA' => 3,
                'BB' => 5,
                'CC' => [
                    'DD' => 4,
                    'EE' => 5
                ]
            ],
            'B' => [
                'BA' => 2
            ]
        ],
        [
            'C' => [
                'CC' => 3,
                'CCC' => 2,
            ],
            'D' => [
                'DD' => 2
            ]
        ],

        5,
        [
            2,
            7
        ]

    ];

    $arrSum = [];

    $count = count($arr);

    for ($i = 0; $i < $count; $i++) {
        $sum = 0;
        if(is_array($arr[$i])) {
            array_walk_recursive($arr[$i], function ($item, $key) use (&$sum) {
                $sum += $item;
            });
        }
        else {
            $sum += $arr[$i];
        }

        $arrSum [] = $sum;
        $sum = 0;
    }

    var_dump($arrSum);

来源：https://stackoverflow.com/questions/49381401/php-how-to-sum-a-value-from-3-dimensional-array